Question: Luis ate 5 slices of cake. Christopher ate 4 slices. If Luis ate $\dfrac{5}{13}$ of the cake, what fraction of the cake was eaten?
Answer: If 5 slices represent $\dfrac{5}{13}$ of the cake, there must have been a total of 13 slices. $\text{fraction of cake eaten} = \dfrac{\text{number of slices eaten}}{\text{number of slices total}}$ They ate ${9}$ out of $13$ slices. They ate $\dfrac{9}{13}$ of the cake.